Intraspecific and interspecific competition for larval nests of the caddisflies Stenopsyche marmorata and Stenopsyche sauteri

Two closely related species of the trichopteran genus Stenopsyche–S. marmorata and S. sauteri– are both widely distributed in Japan, and their larvae often co‐occur in stony stream beds. The larvae make nests by spinning nets in spaces between stones. In this study, I examined the effects of the intruder–resident relationship, bodyweight difference, and species combination on contest outcome in laboratory experiments. In S. marmorata, bodyweight was revealed to be a better predictor of winning a contest than was residency. In S. sauteri, however, there was a prior‐resident effect in the contests, and takeover occurred in a few cases when the intruders were larger than the residents. The duration of agonistic behavior increased as the bodyweight differences between the fighting individuals decreased. In heterospecific contests, outcomes were generally asymmetric: the larvae of S. marmorata (the larger species) rarely intruded into the nest of S. sauteri, while they, in most cases, protected their own nests from intrusion by S. sauteri larvae. In conclusion, the resident wins in both forms of competition when either S. marmorata or S. sauteri is an intruder.     

Genetic differentiation of a European caddisfly: past and present gene flow among fragmented larval habitats

We describe the genetic structure of a freshwater insect species and interpret it in terms of present-day population dynamics and possible postglacial colonization history. The sampling regime represented a large area of the species range in northwest Europe, particularly focusing on Britain, a region relatively neglected in molecular population genetic studies. Plectrocnemia conspersa generally showed low levels of genetic variation across the sampled populations (Nei's D = 0.0138) and subdivision was unrelated to the pattern of the drainage network. However, the results do suggest that populations across the region are not at equilibrium and that British populations still show effects of the recolonization of the species following the last glacial maximum. Levels of genetic diversity were lower in Britain than in mainland Europe. Two-dimensional scaling showed genetic differentiation between major regions and the pattern of genetic diversity indicates a more recent origin of populations in the north and west of the area compared with the south and east. We argue that, despite the highly fragmented larval habitat, dispersal over tens of kilometres is frequent. Over longer distances, however, P. conspersa does still show evidence of founder effects and postglacial range expansion into Britain.     

Factors affecting depth distribution of dragonflies and other benthic insects in a thermally destabilized reservoir

The distribution and abundance of macroinvertebrates along a water depth gradient were studied in thermal and ambient temperature areas of a reservoir in the southeastern United States. Benthic samples were taken at 10 depths (0.16–5 m) during January–April, 1978. Factors affecting the depth distribution of Ceratopogonidae, Chaoboridae, Chironomidae, Ephemeroptera, Odonata, and Trichoptera are discussed. The relationship between abundance of organisms and water depth was more complex than an inverse relationship generally reported in the literature.     

The impacts of habitat disturbance on adult and larval dragonflies (Odonata) in rainforest streams in Sabah,Malaysian Borneo

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Scale dependency of diversity components estimated from primary biodiversity data and distribution maps

Different sources of information about biodiversity may lead to unrealistic or biased estimation of its components, with different patterns according to the scale of analysis. In this study, we analyse patterns of species richness at the local (average alpha) and regional (gamma) scales, and the relationship between them (Whittaker's beta), in central Mexico, using as a source of data for the species' distributions: (1) museum specimen occurrence data for birds, and (2) distribution maps based on ecological niche models developed and refined by experts. We performed analyses at five spatial resolutions (1/32°−1/2°). Scale changes (grain and extent) affected significantly the estimates of average alpha, gamma, and beta. Use of raw occurrence data vs. distribution maps yielded contrasting results, with raw data underestimating alpha and overestimating beta, as functions of area. As regards species–area relationships, our results suggest a natural decomposition of factors into an area-invariant component (related to alpha), and an area dependent factor (related to beta). Most of our results are maintained in a null model that randomizes occurrences without changing observed range-size distributions. From this result we argue that average alpha and Whittaker's beta capture little information about the spatial covariation of species distribution patterns.     

Sarcophagid larval proteins: Partial sequence homologies among three cuticle proteins and related structures of drosophilids

Summary Three structural proteins from the larval cuticle ofSarcophaga bullata have been sequenced at the amino terminus for 30–40 residues. We observed a high degree of homology with related proteins ofDrosophila melanogaster, based on the previous findings of M. Snyder, J. Hirsh, and N. Davidson [(1981) Cell 25:165–177].S. bullata protein SC1 had 65% homology withDrosophila isolate CP1, and SC6 showed 49% homology with CPX and 54% with CP2a. The three sarcophagid polypeptides also resembled each other with respect to mapped products of tryptic cleavage. The sites of posttranslational arylation required for puparium formation, namely histidyl and lysyl residues, were asymmetrically distributed in the sarcophagid samples. In SC1 the bulk of the loci of putative crosslinks lay beyond the 43-residue fragment. In SC6 half the histidines fell within the first 25% of the primary chain.     

Comparison of lepidopteran larval communities among tree species in a temperate deciduous forest, Japan

Abstract.  1. The enormous diversity of phytophagous insects in forest canopies is hypothesised to be supported by the number of herbivorous species per host tree species or host specificity. It is therefore necessary to examine the effect of host plant species on compositional changes in the herbivore communities.
2. The lepidopteran larval communities were examined in the canopies of 10 tree species in a temperate deciduous forest of Japan. The phylogeny and leaf flush phenology of host plant species were taken into account as factors affecting the herbivore community assembly.
3. Examination of seasonal changes in the larval community structures on each tree species showed that larval species richness, abundance, and evenness decreased significantly from spring to summer. Larval species richness and abundance were characterised by family-level phylogenetic differences among tree species, whereas evenness was determined at a higher taxonomic level.
4. Compositional changes in the larval communities among tree species showed a remarkable pattern, with a phylogenetic effect at a high taxonomic level in spring, similar to evenness, but a phenological effect in summer. This suggests that host specificity could support the lepidopteran larval diversity in spring.
5. These results suggest that the differences in host utilisation of the herbivore, which reflects the phylogenetic effect of the host plants, can be important as a factor affecting the diversity of lepidopteran larval communities in temperate forests.     

Patterns of freshwater biodiversity in Europe: lessons from the spring snail genus Bythinella

Aim We analyse patterns of biodiversity in the spring snail genus Bythinella, a group of highly isolated and stenotopic freshwater species. We aim to test: (1) whether there are European areas of increased diversity (i.e. ‘hotspots’), (2) whether the potential hotspots inferred show qualitative differences in biodiversity characteristics such as endemicity, distinctiveness of taxa, age of lineages or degree of fragmentation, and (3) whether these hotspots match the Pleistocene refugia of Bythinella spp. Location Europe, Asia Minor. Methods The analyses are based on genetic data from 717 Bythinella specimens sampled at 194 sites. We used haplotypes as operational units in all analyses. To test hypothesis 1, mean pairwise genetic distances between Bythinella populations within each 1° × 1° geographical grid cell sampled in Europe were calculated. Within individual mountain ranges, grid cells with high diversity were grouped with neighbouring ones and hotspots were identified based on pre‐defined criteria. Then, to test hypothesis 2, different biodiversity indices of these regions were calculated and compared. Finally, to test hypothesis 3, the spatial distribution of the identified hotspots was compared with the known Pleistocene refugia of Bythinella spp. Results Five areas showed increased levels of genetic diversity: the Massif Central/Pyrenees, the western and eastern Alps, and the western and eastern Carpathians. These regions showed qualitative differences in biodiversity, with the eastern Carpathians holding the highest number of (endemic) haplotypes, the oldest and most distinct lineages and the highest degree of fragmentation. Only three of the five detected hotspots matched previously identified Pleistocene refugia for Bythinella spp. Main conclusions The genetic diversity of Bythinella spp. is not randomly distributed throughout Europe. Some of the hotspots we identify coincide with those found in other freshwater taxa; others have not previously been reported. Thus, spring organisms may reflect a unique evolutionary history that is distinct from lentic and lotic taxa. Our findings may be useful for conservation purposes even though the species‐level taxonomy of the genus is still under discussion.     

Environmental drivers of freshwater macrophyte diversity and community composition in calcareous warm‐water rivers of America and Africa

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Revisiting the effect of PCR replication and sequencing depth on biodiversity metrics in environmental DNA metabarcoding

Environmental DNA (eDNA) metabarcoding is an increasingly popular tool for measuring and cataloguing biodiversity. Because the environments and substrates in which DNA is preserved differ considerably, eDNA research often requires bespoke approaches to generating eDNA data. Here, we explore how two experimental choices in eDNA study design—the number of PCR replicates and the depth of sequencing of PCR replicates—influence the composition and consistency of taxa recovered from eDNA extracts. We perform 24 PCR replicates from each of six soil samples using two of the most common metabarcodes for Fungi and Viridiplantae (ITS1 and ITS2), and sequence each replicate to an average depth of ~84,000 reads. We find that PCR replicates are broadly consistent in composition and relative abundance of dominant taxa, but that low abundance taxa are often unique to one or a few PCR replicates. Taxa observed in one out of 24 PCR replicates make up 21–29% of the total taxa detected. We also observe that sequencing depth or rarefaction influences alpha diversity and beta diversity estimates. Read sampling depth influences local contribution to beta diversity, placement in ordinations, and beta dispersion in ordinations. Our results suggest that, because common taxa drive some alpha diversity estimates, few PCR replicates and low read sampling depths may be sufficient for many biological applications of eDNA metabarcoding. However, because rare taxa are recovered stochastically, eDNA metabarcoding may never fully recover the true amplifiable alpha diversity in an eDNA extract. Rare taxa drive PCR replicate outliers of alpha and beta diversity and lead to dispersion differences at different read sampling depths. We conclude that researchers should consider the complexity and unevenness of a community when choosing analytical approaches, read sampling depths, and filtering thresholds to arrive at stable estimates.     

Decoupled responses of biodiversity facets driven from anuran vulnerability to climate and land-use changes

Biodiversity loss not only implies the loss of species but also entails losses in other dimensions of biodiversity, such as functional, phylogenetic and interaction diversity. Yet, each of those facets of biodiversity may respond differently to extinctions. Here, we examine how extinction, driven by climate and land-use changes may affect those different facets of diversity by combining empirical data on anuran–prey interaction networks, species distribution modelling and extinction simulations in assemblages representing four Neotropical ecoregions. We found a mismatch in the response of functional, phylogenetic and interaction diversity to extinction. In spite of high network robustness to extinction, the effects on interaction diversity were stronger than those on phylogenetic and functional diversity, declining linearly with species loss. Although it is often assumed that interaction patterns are reflected by functional diversity, assessing species interactions may be necessary to understand how species loss translates into the loss of ecosystem functions.     

Elevational patterns and hierarchical determinants of biodiversity across microbial taxonomic scales

Microbial biogeography is gaining increasing attention due to recent molecular methodological advance. However, the diversity patterns and their environmental determinants across taxonomic scales are still poorly studied. By sampling along an extensive elevational gradient in subarctic ponds of Finland and Norway, we examined the diversity patterns of aquatic bacteria and fungi from whole community to individual taxa across taxonomic coverage and taxonomic resolutions. We further quantified cross‐phylum congruence in multiple biodiversity metrics and evaluated the relative importance of climate, catchment and local pond variables as the hierarchical drivers of biodiversity across taxonomic scales. Bacterial community showed significantly decreasing elevational patterns in species richness and evenness, and U‐shaped patterns in local contribution to beta diversity (LCBD). Conversely, no significant species richness and evenness patterns were found for fungal community. Elevational patterns in species richness and LCBD, but not in evenness, were congruent across bacterial phyla. When narrowing down the taxonomic scope towards higher resolutions, bacterial diversity showed weaker and more complex elevational patterns. Taxonomic downscaling also indicated a notable change in the relative importance of biodiversity determinants with stronger local environmental filtering, but decreased importance of climatic variables. This suggested that niche conservatism of temperature preference was phylogenetically deeper than that of water chemistry variables. Our results provide novel perspectives for microbial biogeography and highlight the importance of taxonomic scale dependency and hierarchical drivers when modelling biodiversity and species distribution responses to future climatic scenarios.